The overall long-term objective of the proposed is to increase our understanding of the population genetics and modes of evolution of mobile elements in eukaryotes using the P element family as a model system. P elements are one of two transposable element families which are associated with the hybrid dysgenesis syndrome in Drosophila melanogaster and they have many similarities with mobile elements in other higher organisms such as maize. Specific aims are to obtain a thorough understanding of the relationship between the functional and molecular properties of P elements and to determine the extent and nature of the effects of P element sequences on the phenotype of the Drosophila organism. The dynamics of P elements will be investigated in both natural and laboratory populations. The rate and direction of their evolution will be determined in newly invaded populations and factors affecting their regulation will be studied. As essentially experimental approach will be adopted to achieve these goals. Both genetic and biochemical methods will be used to determine the functional and molecular properties of P elements respectively. Informal collaboration with other laboratories employing specialized molecular genetic techniques is planned. With the growing realization of the ubiquity of transposable elements in higher organisms and their role in the induction of mutations, chromosomal abberations and genomic reorganization, there is considerable potential for the application of basic research on transposable elements to various aspects of human health.